Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$103.83	4.158%	$108.1473	$108.15	$108.15	$108.10
Purchase #2	$124.37	13.699%	$141.4074	$141.41	$141.40	$141.40
Purchase #3	$64.52	3.648%	$66.8737	$66.87	$66.85	$66.90
Purchase #4	$31.61	5.462%	$33.3365	$33.34	$33.35	$33.30
Purchase #5	$139.72	13.292%	$158.2916	$158.29	$158.30	$158.30
Purchase #6	$74.67	10.703%	$82.6619	$82.66	$82.65	$82.70
Purchase #7	$232.67	7.827%	$250.8811	$250.88	$250.90	$250.90
7 purchase totals =	$771.39		$841.5995	$841.60	$841.60	$841.60